The present invention relates to a method of writing patterns on a medium, and to a data storage device. More particularly, the invention relates to timing control of pattern writing on a rotating medium.
The devices that use an optical disk, a magnetic tape, or some other form of medium, are known as data storage devices. Among them, a hard-disk drive (HDD) is most commonly used as a storage device in a computer and is one of storage devices essential in current computer systems. In addition, the applications of the HDD are not confined to computer systems. The excellent characteristics of the HDD are increasingly expanding its applications in such products as: moving-picture recording/reproducing devices, car navigation systems, hand-held phones, and removable memories used in digital cameras.
The magnetic disk used in the HDD has a plurality of concentrically formed tracks, and servo data and user data are stored on each track. A head element section formed up of thin-film elements can conduct data read or write processes by accessing desired areas (addresses) in accordance with the servo data. Signals that the head element section has read from the magnetic disk during a data read process are subjected to waveform shaping, decoding, and other required signal processing by a signal-processing circuit and transmitted to a host. Data that has been transferred from the host undergoes similar required processing by the signal processor, and then the data is written on the magnetic disk.
As mentioned above, each track has a user data area into which user data is to be stored, and a servo pattern area into which servo data is to be stored. Servo patterns (hereinafter, called the Product Servo Patterns) each consist of a cylinder ID, a sector number, a burst pattern, and more. The cylinder ID denotes the address of the track, and the sector number denotes a sector address within the track. The burst pattern provides the information of the precise position of a magnetic head with respect to the track.
Product Servo Pattern comprise of multiple sectors which are equally spaced in a circumferential direction on each track. Locations (phases) of the product servo pattern in each sector coincide to each other in the circumferential direction over the whole radius. Data reading from or data writing on the magnetic disk is executed while the position of the magnetic head is being confirmed against the servo data in the rotating state of the magnetic disk.
The Product Servo Patterns are written on the magnetic disk in the factory before the HDD is shipped as a product. Conventional typical writing of Product Servo Patterns is conducted using a servo writer as an external device. After the HDD has been set up on a servo writer, the servo writer positions an internal head of the HDD via a positioner (external positioner) and writes on the magnetic disk the Product Servo Patterns that have been generated by a Product Servo Pattern generator.
Currently, the Product Servo Pattern writing process (Servo Track Write: STW) occupies the main portion in the manufacturing costs of the HDD. Particularly in recent years, the competition in capacity enhancement of the HDD has been intensified, which is accelerating an increase in the TPI (Tracks Per Inch) of the HDD. The increase in TPI means that whereas the total number of tracks on the magnetic disk increases, track width (track pitch) decreases. These tendencies, in turn, are accelerating an increase in STW time and the enhancement of servo writers in precision, thus increasing STW costs. In order to reduce the costs, efforts are being made towards, for example, reduced servo writer costs and a shorter STW time.
Under these circumstances, SSW (Self Servo Write) has been proposed as a new technique. The SSW technique, unlike existing STW, uses only the mechanical sections of the HDD main unit to control the internal spindle motor (SPM) and voice coil motor (VCM) of the HDD from an external circuit and uses the external circuit to write Product Servo Patterns. This reduces the costs of the servo writer.
A known SSW technique is by utilizing the fact that the read element and write element of the head element section differ in radial position (this difference is called the read/write offset). In this SSW technique, patterns that have already been written at the inner or outer circumferential side are positioned by the read element while it is reading each pattern, and the write element writes new patterns on desired tracks spaced through the read/write offset.
During SSW, the Product Servo Patterns on adjacent servo tracks must accurately match in circumferential position. This is because, since the Product Servo Patterns are written so as to partly overlap between adjacent servo tracks, if the phase in a circumferential direction does not mismatch between the patterns on adjacent tracks, signals cancel one another between the written patterns, consequently making necessary pattern writing impossible. In addition, each pattern is preferably written at equal intervals in the circumferential direction to ensure the ease of control.
For SSW, therefore, it is required that the position in the circumferential direction, that is, the timing of writing be accurately controlled during the write processes for the Product Servo Patterns or for other patterns which become the basis for Product Servo Pattern writing. A known technique as in Patent Document 1 (Japanese Patent Laid-Open No. Hei 08-212733) uses the intervals between written timing patterns to conduct write timing corrections intended for circumferential interval control of the patterns during timing pattern propagation in servo writing.
To accurately write multiple patterns on a track, it is necessary to control the SPM precisely and maintain its rotating speed accurately. For example, writing multiple patterns at equal intervals can be accomplished by repeating the equal-interval write process at a constant clock frequency and a constant clock count while maintaining the rotating speed of the SPM accurately. Generally, dedicated external servo writer may achieve such precise control of rotation of the SPM, and thereby, pattern writing at precisely even intervals.
It is possible, as an improved form of conventional SSW, to make the HDD self-write servo patterns on a magnetic disk by using the internal circuit of the HDD. Self-writing of the servo patterns by the internal circuit of the HDD in an autonomous manner eliminates the need for using a dedicated servo writer and thus for a large amount of equipment investment.
Though it is desirable for the normal HDD to conduct the SSW process by using its own internal mechanism/circuit, it is difficult for the HDD, unlike a dedicated external servo writer, to control SPM rotation precisely, so that fluctuations in the rotating speeds of magnetic disks exist (the fluctuations are referred to as rotational jitter). Accordingly, even if pattern writing on a magnetic disk in accordance with a constant clock is attempted, since the nonuniformity of pattern intervals occurs, the patterns cannot be written at equal intervals on the same track, or regardless of whether the pattern intervals become equal or unequal, a phase shift occurs between the patterns on adjacent tracks. The phase shift is also caused by the occurrence of an error such as a time-interval measurement noise error or a jitter error in the clock itself.
The present invention has been made with the above-described situations as its background, and an object of the present invention relate to writing new patterns with more accurate timing by suppressing any effects of unwanted events such as a rotational jitter of a medium or various kinds of signal noise during autonomous pattern writing.